Abstract: Drug abuse and HIV-1 are two linked global health crises. Despite the recognized impact of cocaine abuse on the clinical course of HIV-1-associated neurological disorder (HAND), the mechanisms underlying the ability of cocaine to modulate central nervous system (CNS) pathology remain elusive. Neuroinflammation involving robust microglial activation has emerged as an important phenotype and correlate of HIV infection and drug abuse despite the advent of combined anti-retroviral therapy (cART). The underlying cause of HIV-associated neuroinflammation is likely attributable to the fact that following virus infection and formation of the proviral DNA, cART is ineffective in abrogating the expression of toxic viral gene products such as Tat and gp120, that continue to be present in tissues such as the CNS. Furthermore, similar to HIV positive subjects on cART, SIV- infected rhesus macaques on cART also demonstrate increased glial activation, which was shown to be associated with dysregulation of various signature microRNAs (miRs). Emerging evidence also points to the role of drugs such as cocaine in mediating glial activation with global changes in miRs. In fact, in a recent finding, we demonstrate that cocaine-mediated activation of microglia involves down-regulation of miR-124 expression both in vitro and in vivo. Furthermore, we have also elucidated that HIV Tat mediated microglial migration involves upregulated expression of miR-9 with a concomitant downregulation of its target, monocyte chemotactic protein-induced protein 1 (MCPIP1). We thus hypothesize that both cocaine and HIV Tat modulate increased microglial activation and migration respectively, via two distinct mechanisms: a) cocaine mediates downregulation of miR-124 via DNA methylation of its promoter, leading in turn, to increased TLR4 signaling that culminates into increased microglial activation and, b) exposure of microglia to HIV Tat upregulates the expression of miR-9 leading in turn, to enhanced microglial migration via downregulation of the target MCPIP1. Three experienced PIs (Drs. Buch, Hu, & Guo) will co-lead this project to accomplish the proposed goals. This proposal is responsive to the RFA (RFA-DA-16-012) focusing on epigenomic and non-coding RNA regulation in HIV/AIDS and substance abuse.